库车褶皱冲断带前缘盐层厚度对滑脱褶皱构造特征及演化的影响

库车褶皱冲断带前缘发育一系列滑脱褶皱，虽然卷入变形的新生代地层及底部滑脱层(古近系盐层)相同，但滑脱褶皱的构造特征及演化存在显著差异。文中结合野外地质调查结果以及钻井资料和高品质二维地震反射剖面解析，以南喀背斜和米斯坎塔克背斜为例，估算出盐层初始厚度，并讨论其对于滑脱褶皱样式及其演化过程的影响。结果表明，南喀背斜和米斯坎塔克背斜下伏盐层初始厚度不同，估算出前者厚度介于0.1~0.5 km，主要为0.1~0.3 km，而后者却大约为1.0 km。与此同时，南喀背斜和米斯坎塔克背斜均表现出分段差异变形特征。南喀背斜为低缓的滑脱褶皱，其东段隐伏地下，变形方式为褶皱作用；而西段出露地表，背斜核部发育隐伏的逆冲断层，变形方式为褶皱作用和断层作用。背斜西段平均隆升速率大于东段，导致西段隆升出露地表。米斯坎塔克背斜表现为大规模滑脱褶皱，根据变形特征的不同可以分为3段，东段背斜倾向北，盐岩在其核部及北翼下方聚集加厚；而中-西段背斜倾向南，其中中段背斜核部位置盐岩聚集加厚，两翼下伏盐岩减薄甚至形成盐焊接。而在西段背斜呈箱状，两翼下方盐岩厚度至少为1.0 km。笔者总结出库车褶皱冲断带前缘发育的7种滑脱褶皱变形样式，通过构造分析得出，研究区滑脱褶皱的变形主要受盐层厚度、构造缩短量及盐岩流动变形共同控制，其中盐层厚度起主导作用，控制了滑脱褶皱的发育位置，并影响了滑脱褶皱的变形样式。研究结果将为其他褶皱冲断带中滑脱褶皱的相关研究提供重要参考，特别是在缺少高品质地震资料，或者构造变形强烈、地震资料品质较差的地区。

The impact of salt layer thickness on the structural characteristics and evolution of detachment folds in the leading edge of Kuqa fold and thrust belt

Detachment folds are widely distributed in the leading edge of Kuqa fold and thrust belt (KFTB). Although the Cenozoic sedimentary strata involved into the structural deformation and their underlying basal detachment (Paleogene salt layer) are the same, the structural characteristics and the evolution of detachment folds are quite different. In this paper, on the basis of the field observations and the interpretations of high quality seismic and well data, we demonstrate the initial salt layer thickness and discuss their relations to the deformation styles and the evolution of detachment folds, taking the examples from the Nanka and Misikantage anticlines. The results of our analysis indicate that the initial underlying salt layer of Nanka anticline is about 0.10.5 km in thickness, generally of 0.10.3 km, which is in contrast to the Misikantage anticline with thickness of as much as ~ 1.0 km. Meanwhile, the along strike variations in the structural styles have been observed both in the Nanka and Misikantage anticlines. The Nanka anticline is a low amplitude detachment fold, whose eastern segment is buried under the ground surface and characterized by the folding deformation. However, in its western segment the fold with relative higher average uplift rate is consequently exposed on the surface associated with both folding and thrusting, as evidenced by thrust faults developed at the core of anticline. In contrast, the Misikantage anticline is a large scale detachment fold, which can be divided into three segments of different geometry. The north vergence of the anticline in the eastern segment are different from the south vergence of the anticline in the central and western segments. Meanwhile, thick salt is mainly accumulated underlying the north limb and at the core of anticline in the eastern segment, which is in contrast to the salt accumulated at the core of anticline, thinning towards both limbs and even forming the salt welds in the central segment, and also obviously different from the box fold with underlying salt layer of at least 1 km in thickness in the western segment. In summary, seven distinct deformation styles of detachment folds in the leading edge of KFTB have been demonstrated, and, according to our analysis, the deformation style of detachment fold was strongly affected by the salt layer thickness, compressive shortening and salt flow. Among them, the salt layer thickness was dominative in controlling the deformation style of detachment fold. The results of this study concerning about the structural characteristics and evolution of detachment folds and their controlling factors might be helpful for the investigations of the detachment folds in other fold and thrust belts, especially within the regions without high quality seismic data or poor quality due to intense strutural deformation.